The present invention relates to a small built-in radio communication antenna which is small and light and which has excellent gain and broadband tuning characteristics, and, more particularly, to a small low-posture antenna that is suitable for industrial production.
A whip antenna which resonates at xcex/2 is used as an antenna which sends and receives GHz (gigahertz) class radio waves.
However, when the mechanical length of a whip antenna is about 10 cm, it becomes difficult to handle. Therefore, it has often been used by making it stowable/extendable by forming it into an extendable type or a tilting-down type.
However, in a stowable/extendable type, not only is it troublesome to operate the antenna, but also the antenna may break due to collision with an external obstacle when the antenna is in an extended posture.
To overcome this problem, a built-in antenna which is made short to the order of xcex/4, and which does not need to be extended/stowed has been developed. This technology has been created by the present inventor, and an application thereof is separately being filed by the present applicant (Japanese Patent Application No. 2000-237629). (This application will hereunder be referred to as xe2x80x9cearlier application which is not yet publicly known.xe2x80x9d)
FIG. 9 is a schematic view which is drawn as FIG. 1 in the earlier application which is not yet publicly known.
A plate-shaped antenna 1 having an overall length of xcex/4 is bent into an L shape, with an end 1a at a short side of the antenna 1 being mounted to and supported by a bottom plate 2.
On the other hand, an input end 3b of a xcex/4 antenna exciter 3 is connected to an output end of a high-frequency circuit 4, and an open end 3a thereof opposes and is spaced from an open end 1c of the plate-shaped antenna 1 in order to provide an electrostatic coupling capacity c.
The antenna of the earlier application that is not yet publicly known, shown in FIG. 9, has an overall electrical length of xcex/4, and its mechanical length can be decreased to less than xcex/4. When this antenna is used as a built-in antenna, extending and contracting operations do not need to be carried out, so that this antenna is very convenient to use, and will not break when it collides with an external obstacle. In addition, since the antenna has wideband tuning characteristics and high gain, the antenna provides excellent characteristics.
After filing the application of the above-described invention that is not yet publicly known, the present inventor has promoted experiments and research for practical application. It has been confirmed that, even under practical conditions, the antenna provides the desired advantages. On the other hand, it has been found and confirmed that there is still room for improvement.
This room for improvement will be described below. In order for the antenna device to operate with good characteristics, it is necessary for the electrostatic coupling capacity c to be an appropriate value that realizes a critical coupling state, and for the parallelism and the interval between a long side of the plate-shaped antenna 1, formed into an L shape, and the bottom plate 2 to be proper values.
Under laboratory use conditions, the aforementioned requirements do not give rise to particular problems, but, when such antennas (FIG. 8) are industrially produced in large quantities, it is difficult to maintain uniformity in the qualities of many products (more specifically, the uniformity in the characteristics of the antennas).
This is because it is not easy to restrict with high precision the positions and the postures of such plate-shape antennas 1. which are bent into an L shape by punching out a metal plate into strips, when their short-side ends are mounted to the bottom plate 2.
Further, it is not easy to position with high precision the antenna exciter 3 with respect to the plate-shaped antenna 1.
The present invention has been achieved in view of the above-described problems, and has as its object the provision of a technology which, by improving the antenna of the earlier application which is not yet publicly known, is made suitable for maintaining uniformity in qualities in industrial production and makes it possible to further reduce the height (interval between a plate-shaped antenna and a bottom plate), without impairing characteristic features, such as smallness, not requiring extending and contracting operations, and high performance (particularly, wideband tuning characteristics).
A structure of a method of an invention of claim 1 created to achieve the aforementioned end is that of a method for forming an antenna which is tuned near a wavelength xcex, wherein an antenna pattern which resonates at xcex/4 is formed on a surface of a substrate, wherein the substrate is made to oppose and is supported with respect to a planar portion of a metallic frame, wherein a helical coil which resonates at xcex/4 is supported by the metallic frame, wherein one end of the antenna pattern is connected to and is brought into electrical conduction with the metallic frame, and wherein one end of the helical coil and one end of the antenna pattern are made to oppose each other in order to provide capacitance and the other end of the helical coil is connected to an output end of a high-frequency circuit in order to make the helical coil act as an antenna exciter.
In addition to including the structural requirement of the invention of claim 1. a structure of a method of an invention of claim 2 includes a structural requirement in which, in means for connecting and bringing into electrical conduction the helical coil and the output end of the high-frequency circuit, a core wire of a coaxial cable is connected to and brought into electrical conduction with one end of the helical coil, and an external conductor is connected to and brought into electrical conduction with the metallic frame, and wherein the other end of the core wire of the coaxial cable is connected to the output end of the high-frequency circuit, and the external conductor is connected to a bottom plate of the high-frequency circuit.
A structure of a method of an invention of claim 3 is that of a method for forming an antenna which is tuned near a wavelength xcex, wherein an antenna pattern which resonates at xcex/4 is formed at one end of a surface of a substrate, wherein an exciter pattern which resonates at xcex/4 is formed near the other end of the substrate, wherein the antenna pattern and the exciter pattern are made to oppose each other and to be spaced from each other in order to provide capacitance therebetween, wherein the substrate is supported by a metallic frame having a planar portion that opposes the substrate, and wherein one end of the exciter pattern is connected to an output end of a high-frequency circuit.
In addition to including the structural requirement of the invention of claim 3, a structure of a method of an invention of claim 4 includes a structural requirement in which, in means for connecting and bringing into electrical conduction the exciter pattern and the high-frequency circuit, a core wire of a coaxial cable is connected to and brought into electrical conduction with one end of the xcex/4 exciter pattern and an external conductor is connected to and brought into electrical conduction with the metallic frame. and wherein the other end of the core wire of the coaxial cable is connected to the output end of the high-frequency circuit and the external conductor is connected to a bottom plate of the high-frequency circuit.
In addition to including the structural requirement of either claim 1 or claim 3, a structure of a method of an invention of claim 5 includes a structural requirement in which the antenna pattern generally has a strip shape and has a rectangular or zigzag portion formed on the substrate, and in which the substrate is supported by the metallic frame, and a portion near the zigzag portion is connected to and brought into electrical conduction with the metallic frame.
In addition to including the structural requirement of the invention of either claim 1 or claim 3, a structure of a method of an invention of claim 6 includes a structural requirement in which holes for inserting mounting screws are provided in both end portions of the metallic frame and the mounting screws that have been inserted into the holes are screwed into the bottom plate. so that the metallic frame is secured to and brought into electrical conduction with the bottom plate, or in which ground/mounting terminals which protrude in a direction opposite to xe2x80x9cthe substrate which has the antenna pattern which resonates at xcex/4 formed thereonxe2x80x9d are formed in the both end portions of the metallic frame and the terminals are passed through and soldered to the bottom plate.
In addition to including the structural requirement of the invention of either claim 1 or claim 3, a structure of a method of an invention of claim 7 includes a structural requirement in which a planar portion having a rectangular shape that is substantially the same as that of the substrate having the antenna pattern formed thereon is formed at the metallic frame, in which a portion of the planar portion near an end thereof is bent at a substantially right angle in order to form a standing wall portion and the substrate having the antenna pattern formed thereon is supported near an end of the standing wall portion, and in which the rectangular planar portion is bent at a substantially right angle along a long side thereof, so that a reinforcement edge which functions as a reinforcement rib is formed in order to prevent deformation of the planar portion.
In addition to including the structural requirement of the method of the invention of claim 1, a structure of a method of an invention of claim 8 includes a structural requirement in which the helical coil is wound and formed upon a circular cylindrical bobbin and the bobbin is mounted to the metallic frame, and wherein one end of the substrate having the antenna formed thereon is mounted to and supported by the metallic frame and a portion of the substrate near the other end is mounted to and supported by the bobbin.
A structure of a small low-posture antenna of claim 9 is that of an antenna which is tuned near a wavelength xcex comprising a substrate having an antenna pattern which resonates at xcex/4 formed thereon, a metallic frame mounted to one end of the substrate to support the substrate and connected to and brought into electrical conduction with the antenna pattern, a coil bobbin mounted to the metallic frame, a helical coil which is wound and formed upon the bobbin and which resonates at xcex/4, and a coaxial cable which has a core wire connected to and brought into electrical conduction with one end of the helical coil and which has an external conductor connected to and brought into electrical conduction with the metallic frame, wherein the metallic frame is such as to be capable of being mounted to a bottom plate, and the other end of the helical coil and the antenna pattern oppose each other and are spaced from each other in order to provide capacitance therebetween.
In addition to including the structural requirement of the invention of claim 9, a structure of a small low-posture antenna of claim 10 includes a structural requirement in which, in means for connecting and bringing into electrical conduction the helical coil and an output end of a high-frequency circuit, the core wire of the coaxial cable is connected to and brought into electrical conduction with one end of the helical coil, and the external conductor is connected to and brought into electrical conduction with the metallic frame, and wherein the other end of the core wire of the coaxial cable is connected to the output end of the high-frequency circuit, and the external conductor is connected to the bottom plate of the high-frequency circuit.
A structure of a small low-posture antenna of an invention of claim 11 is that of an antenna which is tuned near a wavelength xcex in which an antenna pattern which resonates at xcex/4 is formed at one end of a surface of a substrate, in which an exciter pattern which resonates at xcex/4 is formed near the other end of the substrate and both of the patterns are made to oppose each other and to be spaced from each other in order to provide capacitance therebetween, in which the substrate is supported by the metallic frame and the antenna pattern is connected to and brought into electrical conduction with the metallic frame, in which an external conductor of a coaxial cable is connected to and brought into electrical conduction with the metallic frame and a core wire of the coaxial cable is connected to and brought into electrical conduction with xe2x80x9ca portion near an end portion situated at the opposite side of a portion where the exciter pattern opposes the antenna patternxe2x80x9d and in which the metallic frame is such as to be capable of being mounted to a bottom plate that is formed on a high-frequency circuit board.
In addition to including the structural requirement of the invention of claim 11, a structure of a small low-posture antenna of an invention of claim 12 includes a structural requirement in which, in means for connecting and bringing into electrical conduction the exciter pattern and a high-frequency circuit, the core wire of the coaxial cable is connected to and brought into electrical conduction with one end of the xcex/4 exciter pattern and the external conductor is connected to and brought into electrical conduction with the metallic frame, and in which the other end of the core wire of the coaxial cable is connected to an output end of the high-frequency circuit and the external conductor is connected to the bottom plate of the high-frequency circuit.
In addition to including the structural requirement of the invention of claim 9 or claim 11, a structure of a small low-posture antenna of an invention of claim 13 includes a structural requirement in which the antenna pattern generally has a strip shape and has a rectangular or zigzag portion formed on the substrate, and in which the substrate is supported by the metallic frame, and a portion near the zigzag portion is connected to and brought into electrical conduction with the metallic frame.
In addition to including the structural requirement of the invention of claim 9 or claim 11, a structure of a small low-posture antenna of an invention of claim 14 includes a structural requirement in which the metallic frame has a portion that has a shape and size similar to those of the substrate, and in which, by mounting screws or mounting ground terminals, both end portions in a longitudinal direction of the portion similar to the substrate are mechanically secured to and are electrically in conduction with the bottom plate.
In addition to including the structural requirement of the invention of claim 9 or claim 11, a structure of a small low-posture antenna of an invention of claim 15 includes a structural requirement in which the metallic frame has a planar portion having a shape and a size that is similar to those of the strip-shaped substrate, in which a portion near an end in a longitudinal direction of the planar portion is bent at a substantially right angle to form a standing wall portion and the strip-shaped substrate is mounted and supported near an end of the standing wall portion, and in which an edge in the longitudinal direction of the planar portion is bent at a substantially right angle, so that the bent portion can function as a reinforcement rib which can prevent deformation of the planar portion.
In addition to including the structural requirement of the invention of claim 9, a structure of a small low-posture antenna of an invention of claim 16 includes a structural requirement in which an engaging hole or notch is formed in a planar portion of the metallic frame and an engaging protrusion is formed at one end surface of the bobbin, in which an engaging hole or notch is formed near an end in a longitudinal direction of the strip-shaped substrate and an engaging protrusion is formed at the other end surface of the bobbin, so that two pairs of xe2x80x9cengaging hole or engaging notch and engaging protrusionsxe2x80x9d are formed, and in which, by rotating the bobbin around a centerline thereof, the two engaging pairs are such as to engage each other or disengage from each other at the same time.
A structure of a small low-posture antenna of an invention of claim 17 is that of an antenna which is tuned near a wavelength xcex comprising a substrate which generally has a strip shape and which has a plate-shaped antenna pattern having a zigzag portion and resonating at xcex/4 formed thereat; a metallic frame which supports the substrate by being mounted to one end in a longitudinal direction of the substrate, the metallic frame being connected and brought into electrical conduction near the zigzag portion of the plate-shaped antenna pattern; a coil bobbin mounted to the metallic frame; a helical coil which is wound and formed upon the bobbin and which resonates at xcex/4; and a coaxial cable having a core wire connected to and brought into electrical conduction with one end of the helical coil and having an external conductor connected to and brought into electrical conduction with the metallic frame; wherein the metallic frame comprises:
a. a planar portion having substantially the same shape and size as the strip-shaped substrate and opposing the substrate so as to be substantially parallel thereto;
b. an extending portion which is adjacent to a long side of the strip-shaped planar portion and which extends along the same plane in a widthwise direction thereof;
c. a reinforcement edge formed by bending most of a peripheral portion of a rectangular plate-shaped portion, where the planar portion and the extending portion are integrally consecutively formed, in a direction opposite to the substrate; and
d. a bottom plate mounting screw through hole formed in the extending portion;
wherein the other end of the helical coil and the plate-shaped antenna pattern are made to oppose each other and to be spaced from each other in order to provide capacitance therebetween.